1. Technical Field
The present invention relates to a lens actuating module to actuate a lens barrel in an optical axis direction, and more particularly, to a lens actuating module that has a simplified structure to transmit a driving force of a piezoelectric actuator to a lens barrel, and can achieve miniaturization and minimize limitation on a migration length of the lens barrel and a tilting phenomenon around an optical axis when the lens barrel is actuated.
2. Description of the Related Art
With the recent development of optics, optical instruments such as cameras, camcorders, and small camera modules for mobile devices have been developed around high-pixel devices of 7,000,000 or more pixels and also have been developed to be able to perform additional functions such as auto focusing and optical zooming.
Such optical instruments realize the zoom-function or the auto-focusing by changing a relative distance of a lens by vertically moving the lens, and include a lens conveyance device to vertically actuate the lens or a lens barrel in which the lens is mounted.
The optical instruments having such additional functions increase the number of parts embedded in a camera module since the lens is conveyed using an electromagnetic motor, and as a result, an entire size thereof may be unavoidably larger than a general camera module.
Accordingly, when the camera module is to be mounted in a limited space such as a mobile terminal, it is difficult to assembly the camera module due to an insufficient space in a body of the terminal to mount the camera module.
FIG. 1 is a view of a related art lens actuating structure, which is disclosed in U.S. Pat. No. 6,268,970, entitled ‘Zoom Lens Barrel’. The related art lens actuating apparatus includes frames to support lens groups 120, 130, and 140 and cam tubes 160 and 170 to support the frames. The cam tubes function to allow the frames to move lenses in an axis direction and are actuated by a driving actuator 110.
According to a zooming method of this cam structure, a relative position of each lens is determined by the shape of the cam in the zoom operation. As such, a focus lens and an actuating unit for focusing at a specific ratio are additionally required and an actuating mechanism such as a final reduction gear and a lens holding structure moving along the cam may be complicated.
FIG. 2 is a view of another related art lens actuating structure, which is disclosed in Korean Patent Laid-Open Publication No. 2000-55180, entitled “Zoom Lens Mechanism of Camera”. In this disclosure, a fixing lens group 201 comprising a plurality of lenses is mounted in a camera body 200. The camera body 200 has a storage space formed therein and a zoom motor 203 is stored in the storage space. A guide screw 205 is connected to a shaft of the zoom motor 203 and a screw ridge and a screw groove are formed along an outer circumference of the guide screw 205. Also, a clip 207 is connected to the outer circumference of the guide screw 205 to transmit a driving force. The clip 207 has a corresponding screw ridge and a corresponding screw groove formed on one side thereof contacting the guide screw 205, so that the one side of the clip 207 is engaged with the screw ridge and the screw groove of the guide screw 205. The other side of the clip 207 is engaged with a zoom barrel 209. The zoom barrel 209 is connected to a moving lens group 202. The zoom barrel 209 is slidably connected to a guide shaft 211 arranged in an optical axis direction so that the zoom barrel 209 slides along the guide shaft in the optical axis direction.
In a zoom lens mechanism of the camera described above, when the zoom motor 203 is rotated, the guide screw 205 is also rotated. After that, the guide screw 205 is rotated and its rotational force is converted into a linear motion through the clip 207. Accordingly, the clip 207 linearly moves in the optical axis direction. As the clip 207 linearly moves, the zoom barrel 209 moves in the optical axis direction. When the zoom barrel 209 moves in the optical axis direction, a portion of the zoom barrel 209 contacting the guide shaft 211 slides so that the zoom barrel 209 reciprocates in the optical axis direction within a predetermined section.
Since the related art zoom lens mechanism described above uses an electromagnetic motor, there is a problem in that an electromagnetic wave occurs. As such, there is a problem in that use of the zoom lens mechanism in a small communication device is limited. Also, when the electromagnetic motor is used, a final reduction gear is used but complicates a mechanical structure. Also, there is a problem in that the zoom lens and the focusing lens should be independently moved in order to perform focusing.
Recently, in order to solve the above problems and use the zooming function in smaller optical devices, micro-optical zoom instruments have been developed. The micro-optical mechanism is increasingly using an intelligent element such as a piezoelectric element, rather than using a related art actuating method by the electromagnetic motor. By substituting the related art motor actuating method, the actuating structure to actuate the lens can be simplified and high efficiency can be achieved by directly actuating.
A zoom lens device using such a piezoelectric element is illustrated in FIGS. 3 and 4. FIG. 3 is a view of still another lens actuating structure disclosed in U.S. Pat. No. 6,215,605, entitled ‘Driving Device’. The related art lens actuating device fixes piezoelectric elements 311 and 312 to base blocks 321 and 322 and transmit displacement to actuating round bars 316 and 317, and conveys lenses L2 and L4 by a preload occurring in slide parts 331a and 332a, an inertial force of the lens holder 331 and 332, and an acceleration effect. According to a waveform of a pressure that the piezoelectric element 312 has, the lens holder is conveyed along with the round bar or conveyed by a motion in which the lens holder slides and stays in position, and may also be conveyed bi-directionally.
In practice, the lens actuating device of FIG. 3 may be arranged in a pattern and used as in FIG. 4. At this time, if displacement of one of the neighboring piezoelectric elements 311a and 311b is transmitted through the base block 313, the displacement may be transmitted to another lens. Therefore, a recess 313g is formed on the base block 313 to prevent the displacement from being transmitted between the piezoelectric elements. However, a process of forming this recess may make the structure more complicated and causes difficulty in processing. Also, a displacement interference problem between the piezoelectric elements cannot be completely solved.
Also, a length of the actuating round bars 316 and 317, which are moved forwards and backwards by the piezoelectric element to convey the lens, is limited by a size of the piezoelectric element, and this limitation on the length of the actuating round bar results in limitation of a lens conveyance length, thereby affecting performance of a product.
Also, in this case, since the actuating round bar is fundamentally fixed, it is impossible to change a length of a body tube in which the lens is embedded, and, since an extra space for actuating elements is required besides the space for the conveyance length of the lens, it is difficult to miniaturize the entire size of the device. Also, since the actuating round bar supports only one end of the lens part, asymmetrical displacement of the lens occurs in the actuating operation and thus may cause unstable actuating.